Rollout observability: GRPO uploads 1-2 rollouts per step to W&B

Currently NeMo RL will [dump all the GRPO train rollouts to disk](https://github.com/NVIDIA-NeMo/RL/blob/main/nemo_rl/algorithms/grpo.py#L781) (thank you @terrykong for the pointer).

However, it would be great to have a more accessible way of getting rollout observability, namely in W&B. We should upload a small sample of rollouts to W&B (like the actual trajectories not just statistics). It can help catch sneaky and scary vllm issues like this one (found and shared by @ertkonuk) https://github.com/vllm-project/vllm/issues/17652